Differential pressure transmitter having an integral flame arresting body and overrange diaphragm

ABSTRACT

A pressure transmitter apparatus having a Unitary body portion, separate diaphragms and flange elements and disposed within the body, a first and second normally vertical pressure passage. The first and second pressure passageways communicate respectively between first and second pressure openings extending-normally horizontally through the body portion, and a transducer mounting element. The mounting element, coupled to the body portion and located above the pressure passageways, mounts a transducer that generates a differential pressure signal. One or a pair of diaphragm elements are configured to form first and second process diaphragms, closing first and second pressure openings. The flange element overlies the diaphragm element and is removably and replaceably secured to the body portion. The pressure transmitter also includes a flame retardation element that is disposed within at least one of the pressure passageways, and an overrange protection element, integrally arranged with the unitary body portion, that protects the transducer from overrange pressure fluctuations. Special flange plane geometries optimize size and sensitivity of isolation diaphragms.

BACKGROUND OF THE INVENTION

This invention relates to process control devices, and, moreparticularly, to improvements in differential pressure transmitters.Differential pressure transmitters measure the difference between twopressures and produce an output signal, typically with a display,responsive to the measurement.

Differential pressure transmitters are commonly used in process controlsystems that require pressure measurements, or measurements of othervariables associated with gases and liquids, e.g., flow rates. A typicaldifferential pressure transmitter has two process diaphragms, eachexposed to one of two fluid pressures that are to be compared, and has atransducer. An inert fill fluid is provided in a closed chamber betweeneach process diaphragm and the transducer, to transmit pressures fromthe process fluids to the transducer. Each process diaphragm deflects inresponse to the pressure of one fluid, as applied from an input processline. The transducer responds to the difference between the twopressures of the process fluid, and produces electrical output signalsfor indication or control. Pressure transmitters that produce electricaloutput signals often include electronic circuitry to process thetransducer signal and to display it by way of a read-out meter, and/orto apply the processed signal to a computer or other electronic device.

Two conventional structural types of pressure transmitters are known:planar designs in which the process diaphragms share the same plane, andbi-planar designs in which the process diaphragms are in differentplanes and are disposed back-to-back. Conventional planar transmittersgenerally have an electronics housing that extends horizontally when thetransmitter is oriented so that the plane of the process diaphragms isvertical. This configuration can require special hardware to mount thetransmitter. Additionally, the electronics housing is displaced from thediaphragm plane in such a way that a read-out meter on the housing isoften difficult to see.

Another drawback of conventional planar transmitters is that theelectronic circuitry is located close to hot process lines.Specifically, in one prior configuration, the differential pressuretransmitter is close to the high pressure and low pressure input processlines. These process lines can radiate heat to the transmitterelectronics, thereby creating a hot operating environment. Thus, thetransmitter is more susceptible to electrical malfunctions.Additionally, exposing the electronics to unnecessary elevatedtemperatures reduces the life of the electrical components.

A further drawback of prior transmitters is that the conventionaltransmitter housing assembly limits the size of the process diaphragms.A large diaphragm diameter is advantageous because it has acorrespondingly low spring rate and hence aids high measuringsensitivity. The diaphragm volumetric spring rate is inverselyproportional to the sixth power of the diameter of the diaphragm.However, prior pressure transmitter structures restrict the diameter ofthe process diaphragms to avoid undue size, which leads to a relativelylarge diaphragm spring rate.

Prior pressure transmitters accordingly resort to thin diaphragms, toachieve a usable spring rate. This, in turn, presents a risk ofdiaphragm leakage, which is a serious problem.

Conventional planar pressure transmitters endeavor to circumvent theforegoing mounting problems by using a flange adapter, in conjunctionwith the existing assembly that mounts the pressure transmitter.However, this solution adds weight and cost to the system.

Conventional bi-planar transmitters are relatively heavy and relativelycostly. The additional weight stems at least in part from large dualprocess covers that mount over the process diaphragms, and from theweight of the associated cover mounting hardware.

Another drawback of both the conventional designs is that the electroniccircuitry is susceptible to fluid noise, such as mechanical shocks, pipevibrations and like mechanical disturbances. Consequently, the pressuretransmitters are susceptible to producing measurement errors whenmechanical disturbances occur.

Due to the foregoing and other shortcomings of conventional pressuretransmitters, an object of this invention is to provide a robustdifferential pressure transmitter that is relatively light in weight andrelatively low in cost.

Another object of the invention is to provide a pressure transmitterthat has a read-out indicator that is relatively easy to view.

Still another object of the invention is to provide a transmitterhousing of relatively small size that mounts process diaphragms ofrelatively large diameter.

Yet another object of the invention is to provide a transmitter housingthat is relatively easy to install and relatively easy to mount.

A further object of the invention is to provide a pressure transmitterthat shields electronic components therein from the elevatedtemperatures of hot process lines, and hence maintains the components ina relatively cool environment.

It is also an object of the invention to provide pressure transmittersthat operate with minimal loss of performance when measuring fluidssubjected to vibration and other mechanical noise.

Other general and specific objects of this invention will in part beobvious and in part be evident from the drawings and description whichfollow.

SUMMARY OF THE INVENTION

This invention attains the foregoing and other objects with a pressuretransmitter having a body portion, a diaphragm element, a flangeelement, and first and second pressure passages. The body portion isgenerally mounted upright and includes, in that orientation, a verticalsurface apertured with first and second pressure openings located atsubstantially the same vertical location. A transducer mounting elementis coupled to the body portion and is located above the pressureopenings. The diaphragm element is configured to form first and secondprocess diaphragms respectively closing the first and second pressureopenings.

This structure, in one embodiment, includes integral ribbed elementsthat provide support and add structural stiffening to the body portion.The body portion preferably has a neck portion that mounts thetransducer mounting element to the body portion and that providesthermal isolation therebetween.

According to one aspect of the invention, the flange element overliesthe diaphragm element and is removably and replaceably secured to thebody portion. The flange element is configured to form first and secondpressure ports that couple fluids in first and second pressure inputlines to the first and second process diaphragms, respectively.

The first and second pressure passages extend at least partly within thebody portion, and communicate respectively between the first and secondpressure openings and the transducer mounting element. The pressuretransmitter according to the invention has a flame retardation elementdisposed in at least one of the first and second pressure passages to bein the fluid path between a sensor element in the transducer mountingportion and a process input line. The flame retardation element thusintroduces a flame barrier between the mounted sensor element and aprocess fluid being measured.

According to further aspects of the invention, the transducer mountingelement mounts a sensor element that is in fluid communication with thefirst and second pressure passageways and that is located, in theupright orientation of the body portion, above the process diaphragms.The sensor element includes a transducer, located at least partlybetween opposed first and second faces of the sensor element, forgenerating a differential pressure signal. The transducer responds tothe difference in pressure between the pressures applied to the firstand second pressure ports.

The sensor element preferably has an overrange protection element thatprotects the transducer from overrange pressure fluctuations. In apreferred embodiment, the overrange protection element overlies at leastthe first pressure passageway, and is integral with the body portion.

According to other aspects of the invention, the body portion preferablyis a unitary structure, and preferably includes a support element forremovably and replaceably attaching the body portion to a mounting pipeor other external transmitter support structure.

In one preferred embodiment of a pressure transmitter according to theinvention, the body portion is configured with the first and secondpressure openings oppositely arranged and substantially parallel to eachother. In one embodiment, for example, the pressure openings arearranged back to back. The flange element includes first and secondprocess covers that respectively overlie the first and second processdiaphragms. Fastener elements, typically threaded such as machine bolts,secure each process cover to the body portion.

In another preferred embodiment of a pressure transmitter according tothe invention, the first and second pressure openings are planar and arelocated horizontally side by side. In this embodiment, the processdiaphragms of the diaphragm element, which overlies the first and secondpressure openings, are formed in the same plane. To mount the flangeelement, the body portion has fastener-receiving apertures preferablylocated at least at two corners of a path bounding a non-squarequadrilateral. Fastener elements in these apertures removably andreplaceably secure the flange element to the body portion. In onepreferred embodiment, the fastener-receiving apertures are located ateach of four corners of the non-square quadrilateral. One preferred formof the quadrilateral is a parallelogram having an acute included angleof typically between 30 and 40 degrees. In a preferred configuration,the acute angle is about 34 degrees.

The foregoing location of the fasteners and apertures, i.e., at comersof a non-square quadrilateral, accommodates large diameter processdiaphragms in a relatively small space. It thus enables the pressuretransmitter to operate with relatively high sensitivity and yet haverelatively small size.

The body portion of the pressure transmitter according to the latterpreferred embodiment has a web-like structure that forms, in an uprightorientation, a vertically extending and planar front surface spaced froma rear face. Fastener receiving apertures extend through the web-likestructure, i.e. between the front surface and the rear face, and partlythrough the flange element. This arrangement allows the fastenerelements to mount from the rear face of the web-like structure to securethe flange element to the front surface of the body portion.

According to still further aspects of the invention, the flameretardation element and the overrange protection element are, fluidwise,connected in series. The overrange protection element preferablyoverlies the flame retardation element that is disposed in the firstpressure passageway. This configuration provides a hydraulic assemblythat dampens fluid noise.

These structural features of the differential pressure transmitter, andother features set forth below, attain a pressure transmitter that iscompact, relatively light weight, relatively low in cost, and relativelyeasy to manufacture. Further, the pressure transmitter can readily mounta read-out meter disposed above the first and second pressure openings,where it is easy to view. Other features of the planar pressuretransmitter include a housing of relatively small size that accommodatesprocess diaphragms having relatively large diameters. This increase inthe process diaphragm diameter reduces the diaphragm spring rate,thereby improving the accuracy of the pressure measurements.

These and other aspects of the invention are evident in the drawings andin the description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following description and apparentfrom the accompanying drawings, in which like reference characters referto the same parts throughout the different views. The drawingsillustrate principles of the invention and, although not to scale, showrelative dimensions.

FIG. 1 is a perspective view of the bi-planar pressure transmitter ofFIGS. 9 and 10:

FIG. 2 is a perspective view of a pressure transmitter according to oneembodiment of the invention with associated mounting hardware;

FIG. 3 is a fragmentary perspective view of the pressure transmitter ofFIG. 2;

FIG. 4 is an exploded view of the pressure transmitter of FIG. 2;

FIG. 5 is a perspective view of the flange shown in FIG. 4;

FIG. 6 is a fragmentary diagrammatic view, partly broken away, of thepressure transmitter of FIG. 4 with elements of the sensor assembly 80diagrammatically relocated;

FIG. 7 is a further exploded view of selected parts of the pressuretransmitter of FIG. 3;

FIG. 8 is a diagrammatic sectional view of a fragment of the pressuretransmitter of FIG. 3, with elements diagrammatically relocated, showingthe fill fluid paths of the high and low pressure sides of thetransmitter;

FIG. 9 is an exploded view of a preferred embodiment of a bi-planarpressure transmitter according to the invention;

FIG. 10 is a diagrammatic elevation view, in section, of the pressuretransmitter of FIG. 9, as assembled and with elements diagrammaticallyrelocated;

FIG. 11 shows the pressure transmitter of FIG. 1 connected with aprocess pipe and oriented for purging gas; and

FIG. 12 shows the pressure transmitter of FIG. 1 connected with aprocess pipe and oriented for draining liquid.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The pressure transmitter of the first embodiment of the presentinvention determines the pressure difference between two input processlines. The transmitter includes a sensor body having a flange portionand a web portion and a pair of planar openings each closed by anisolation diaphragm. The diaphragms are in pressure communication with asensor element by way of an inert fill fluid. The pressure inputs applya pressure to the diaphragms, which is transmitted to a sensor elementby the fill fluid. The sensor element generates a signal, in response tothe applied pressures, indicative of the pressure difference between thetwo pressure inputs. The sensor body employs a diagonal bolt-holeconfiguration that accommodates correspondingly large diaphragms. Thelarger diaphragms have a correspondingly lower spring rate, and thushave a higher measuring sensitivity.

The pressure transmitter also mounts a sensor assembly uppermost on thesensor body that includes an integrally mounted overrange diaphragm. Theoverrange diaphragm protects the sensor element mounted within thesensor assembly from overrange pressure conditions. The sensor body alsopresents high thermal resistance between the input process lines and thesensor assembly, shielding the sensor and associated electronics fromundesirable elevated temperatures.

The bolt-holes of the transmitter further mount fasteners that areenclosed or shrouded along the fastener length by the sensor body. Theshrouded bolts help prevent the leakage of process fluid applied to thepressure ports by maintaining the temperature along the length of thebolt at or near the temperature of the sensor body.

FIG. 2 shows a planar differential pressure transmitter 10 that measuresthe difference in pressure between two pressure inputs, i.e. between twodifferent fluid pressures, coupled to two input process connectors18,18. The pressure transmitter 10 has a flange 14 that receives the twopressure inputs, e.g., process lines, by way of the process connectors18, and has a unitary body element 16 that assembles with the flange 14.In this arrangement, the unitary body element 16 conveys pressures,which are responsive to the two pressure inputs, to a transducer mountedwith the body element 16, and shown in FIG. 4 as a sensing assembly 84.In response, the transducer produces a signal indicative of thedifference in pressure between the two inputs. Electronic circuitrywithin an electronic housing 13 processes the transducer signal, andtypically includes an output display 12. The housing 13 mounts on thebody element 16.

The transmitter 10 mounts to a mounting bracket 20 that secures to astationary support 19 by a mounting U-bolt 21 and associated nuts. Theillustrated transmitter 10 also has a pair of support elements, shown asribbed mounting supports 22, FIG. 7, that removably and replaceablysecure the transmitter 10 to the mounting bracket 20.

The assembled flange 14 and body element 16 of the transmitter 10 form asensor assembly 15 that, as shown in FIG. 3, has first and secondpressure ports 24A and 24B extending through the flange 14. Threadedbolt-holes 26 receive the fasteners of the process connectors 18, FIG.2. The housing is usually installed in the upright orientation shown,where the pressure ports are horizontally spaced apart and are at thesame elevation.

The body element 16 has an integral neck portion 28 that terminates in atransducer mounting portion 30 disposed uppermost on the body element16. The illustrated mounting portion 30 has a first annular surface 30Astepped below a concentric second surface 30B. An eccentric tubularmount 30C extends upward from the second surface 30B. In an alternateembodiment, the mount 30C can have a shape complementary to that shownin FIG. 9. The illustrated surfaces 30A and 30B are concentric with anormally vertical axis 23, and the mount 30C is offset from that axis.The floor 30D of the mount 34, illustrated as formed by the secondsurface 30B, is convoluted, as shown in FIGS. 3 and 4; illustrativelywith concentric and rounded crests and troughs. The neck portion 28 hasa reduced cross-section in a plane transverse to the axis 23, to retardthe conduction of heat from the pressure inputs below the neck to theelectronic housing 13, to protect the sensitive electronic circuitrytherein, and to the sensing assembly 84, both of which are mounted abovethe neck portion. A void in the structure of the neck portion 28, formedby at least one thermal resistance chamber 29 shown in FIG. 6, furtherreduces the neck cross-section to enhance this thermal isolation. Theneck portion 28 thus provides secure mechanical support on the bodyportion for the transducer mounting portion 30 and for the housing 13,and yet presents a path of relatively high thermal resistance betweenthe sensor assembly 15 and the electronic housing 13.

With further reference to FIGS. 2 and 3, the illustrated meter housing13 seats on the sensor assembly 15 by fitting onto a mounting collar 13Ain the annular shelf formed by the first and second surfaces 30A and30B. In a preferred embodiment, the mounting collar 13A is welded to thetransducer mounting portion 30 of the body portion, along the firstannular surface 30A. This collar 13A retards the conduction of heat fromthe pressure inputs to the electronic housing 13, and thus to the heatsensitive electronic circuitry housed therein.

With reference to FIGS. 3 and 6, first and second pressure passageways36 and 38 open to the second surface 30B and to the floor 30D,respectively, of the mounting portion 30 and extend vertically downwardinto the body element 16. The pressure passageways 36, 38 communicate,respectively, with transverse and hence horizontally-extending first andsecond pressure openings 34 and 35 (FIG. 8) in the body element 16. Thepressure passageways 36, 38, along with the openings 34 and 35,communicate the pressures applied at the input pressure ports 24A, 24Bto the mounting portion 30, for application to the sensing element 89.

Ventilation apertures 40A and 40B, shown in FIGS. 3, 4, 5, and 7, extendwithin the flange 14, transverse to and in communication with thepressure ports 24A and 24B, respectively. The ventilation apertures 40Aand 40B allow fluids to be purged from the transmitter 10. In theupright orientation of the sensor assembly 15, the apertures 40A and 40Band the ports 24A and 24B extend horizontally. The ventilation aperturesare closed, e.g. with threaded plugs 74, during operation of thetransmitter 10.

Referring to FIGS. 4 and 8, the illustrated body element 16 is machinedfrom a single cast metal body. The body element 16 is structured with anormally vertical, relatively thin web 44. A front face 44A of the web44 is substantially planar and has two circular recesses 41A and 41B,each illustrated with concentric circular convolutions. The recesses areapertured with the first and second pressure openings 34,35 (FIG. 8),respectively, which provide pressure communication between the recesses41A and 41B and the pressure passageways 36, 38.

The illustrated body element 16 has four bolt holes 42 that extendthrough the web 44. The bolt holes 42 are located at the comers of apath that bounds a non-square quadrilateral. In a preferred embodimentof the invention, as shown in FIG. 4, the bolt holes 42 are located atthe corners of a parallelogram, indicated with the path 16B (shown inbroken lines). The parallelogram has acute included angles ranging fromabout 30° to about 40°, and has a preferred included acute angle ofabout 34°. This specific configuration accommodates correspondinglylarge process diaphragms.

The pair of ribbed mounting supports 22 (FIG. 7) project horizontallyfrom the back face 44B of the normally vertical web 44. The mountingsupports are configured as shown to function as mounts and as structuralstiffeners for the body element 16, i.e. they stiffen the web 44 anddistribute stresses throughout the body 16.

The flange 14, shown in FIGS. 4, 5 and 7, is preferably a one-piecemachined metal casting apertured with the pressure ports 24A and 24B. Arear face 14B of the flange 14, which faces toward the body element 16in the assembled transmitter 10, is recessed with substantially circularchambers 61 and 62 in fluid communication with 24A and 24B that, in theassembled housing 15, overly the convoluted recesses 41A and 41B of thebody element 16. Gasket-seating grooves 59,59 are concentric withchambers 61,62 and seat deformable gaskets 50,50. Threaded apertures 60are formed partly through the flange 14 and receive bolts 64. Theapertures 60 are located to align with the holes 42 of the body element16.

The flange 14 and the body element 16 each have four bolt shrouds 14Cand 16C, respectively, each of which encloses and thereby shrouds a bolt64 substantially along its entire length. The flange and body elementshrouds form a continuous enclosure over each bolt 64 along the passagethereof between the two assembled transmitter constituents 14 and 16.Fully shrouding each bolt maintains an axially constant temperaturealong the bolt length, enhancing the operational features thereof. Thebenefits of this feature include a reduction in the occurrence ofleakage of process fluid applied to the pressure ports 24A and 24B dueto the reduction of thermal loosening or corrosion in the bolts.

The illustrated ventilation apertures 40A,40B, extend within the flange14 between the peripheral surface on either side of the flange 14 andthe chambers 61 and 62, respectively. A threaded venting body 74,apertured with a central passageway 74A, seats within each ventilationaperture. A ventilation plug 74B removably and replaceably seats withinthe central passageway 74A, for selectively sealing the ventilationaperture closed, and alternatively for opening it for venting fluidcarried to the flange 14 by the pressure ports 24A and 24B.

As best shown in FIG. 5, the ventilation apertures 40A,40B are coaxialalong an axis 52 that is transverse to the axes 53A and 53B of thepressure ports 24A and 24B, respectively. The apertures 40A,40Bintersect chambers 61,62, respectively, and extend between theperipheral faces of the flange 14 and the chambers 61,62 along ageometrical chord that is offset from a horizontal diameter of thecross-section of the illustrated chambers.

When the flange 14 is assembled with the body portion 16 in theillustrated upright orientation, each ventilation aperture opens ontoits corresponding chamber above the middle of the chamber. Thisorientation allows gases to be purged from the chamber when theventilation plug 74B that seals the ventilation aperture is removed.Conversely, when the flange 14 is inverted, the ventilation aperturesare disposed below the middle of the chambers 61,62. In thisorientation, the apertures can be used to drain liquids, includingcondensate, from the chambers. The flange 14 preferably bears anorientation indicator 141 on an outer surface to be visually exposed andlocated corresponding to the illustrated vertically offcenter locationof the apertures 40A and 40B. Visual inspection of the indicator thusreveals whether the flange is assembled for venting, or alternatively,for draining.

A front face 14A (FIG. 4) of the flange 14, which faces away from thebody element 16 in the assembled transmitter, forms two process bosses54 and 56 and is apertured with the threaded bolt-holes 26. The processconnectors 18,18 (FIG. 2) seat on the process bosses 54, 56, and aresecured by bolts, FIG. 2, threaded into the bolt holes 26. The processconnectors 18,18 couple the pressure ports 24A, 24B to high pressure andlow pressure input process lines (FIG. 2). In a preferred embodiment,the process connectors 18,18 couple the high pressure input line to thepressure port 24B, and the low pressure input line to the pressure port24A.

The FIG. 4 exploded view of the pressure transmitter 10 shows a thin,flat diaphragm plate 46, that is configured complementary to the webfront face 44A of the body element 16, and which overlies that face,thus covering the convoluted recesses 41A, 4 lB. The diaphragm plate 46has punched holes at locations complementary to the bolt-holes 42. Thediaphragm plate 46 forms a planar pair of diaphragms 46A and 46B (FIG.8) at the locations of the convoluted recesses.

With reference to FIGS. 3, 4, and 8, when the sensor assembly 15 isassembled and secured with the rear-mounting bolts 64, the twodiaphragms 46A and 46B are formed from the portions of the diaphragmplate 46 overlying the convoluted recesses 41A and 41B of the bodyelement 16. The diaphragms 46A and 46B preferably are shaped withconcentric circular convolutions as shown in FIG. 8, which generallyconform to and match, and are in registration with the convolutions ofthe recesses 41A and 41B. Further, in a preferred embodiment asillustrated, the two diaphragms 46A, 46B are formed from the samediaphragm plate, to attain closely matched diaphragm performancecharacteristics. Although the illustrated embodiment employs a singlediaphragm plate, those skilled in the art will recognize that separatediaphragms can be employed.

With further references to FIG. 4, a thin, flat weld plate 48, alsoconfigured similar to the face 44A of the body element 16, overlies theexposed front face of the diaphragm plate 46. The weld plate 48 isapertured with holes aligned with the bolt holes and preferably has aset of two circular openings 48A and 48B, each having a diameter D1equal to or slightly smaller than the diameter of the convolutedrecesses 41A, 4 lB. In a preferred assembly of the sensor assembly 15(FIG. 3 ), the weld plate 48 hermetically seals the diaphragm plate 46to the body 16, as by laser welding the periphery of the weld plate 48and the circumference of the circular openings 48A and 48B to thediaphragm plate 46 and to body element 16. The deformable gaskets 50,50mount over the welds formed around the openings 48A and 48B, andpreferably the circumference of each is within the weld path at eachopening 48A and 48B, to ensure hermetic sealing and to prevent theprocess medium from degrading, e.g., chemically attacking, the weld.

The diameter of each chamber 61 and 62 of the rear face 14B of theflange 14 is preferably equal to or slightly less than the diameter D1of the weld plate openings 48A and 48B. In a preferred embodiment, theflange chambers 61 and 62 allow the input process medium applied by eachprocess connector 18,18 to act upon the entire area of the diaphragmplate which overlies the convoluted regions, e.g., to act upon theentire areas of the diaphragms 46A and 46B circumscribed by the chambers61,62.

The illustrated flange 14 has a peripheral shape generally complementaryto the weld plate 48, the diaphragm plate 46, and the web face 44A ofthe body element 16. This illustrated axially successive assemblagesecures the diaphragm plate 46, the weld plate 48, and the gaskets 50between the body element 16 and the flange 14, FIGS. 3 and 4. Thediaphragm plate 46, the weld plate 48, the body element 16 and theflange 14, can be made from a variety of corrosion resistant materials,such as stainless steel.

Referring again to FIG. 4, flame arrestors 68 and 70 are seated in thefirst and second pressure passageways 36,38, respectively, and flamearrestor 68 is secured to the body element 16, for example bytack-welding, along the mouth 36A of the pressure passageway 36. Theflame arrestors are axially spaced from the walls of the passageways toform a gap having a selected size. In the illustrated embodiment, flamearrestor 70 is seated in the second pressure passageway 38 and is weldedcompletely about the passageway mouth 38A, thus forming a fluid-tightseal. Each flame arrestor 68 and 70 functions as a flame barrier bypreventing a flame, in the unlikely event one is ignited by electricalsignals generated in the sensor assembly, from traveling down thepressure passageways 36,38, and into the input process lines. The flamearrestors also function as flow resistors that dampen fluid noiseresulting from pipe vibrations, shock, flow turbulence and likemechanical disturbances.

The illustrated arrestor 70, in addition, has a cylindrical stem-likeprotrusion 70A at the upper end and a concentric longitudinallyextending cylindrical main body 70B. The arrestor 70 also has a centralbore 70C, FIG. 6, extending through the protrusion 70A and partly intothe main body 70B. A normally-horizontal cylindrical channel 70D in thearrestor extends transverse to and bisects the central bore 70C. Thehorizontal channel 70D and the longitudinal bore 70C provide apassageway through which a fill fluid, e.g., hydraulic oil, passesaround the flame arrestor body 70B into the pressure passageway 38. Theflame arrestors 68 and 70 and the controlled gap effectively extinguishany flame front passing through the narrow passages. This occurs sincethe gap space cannot support a temperature sufficient to sustain theflame front.

A sensor assembly 80, illustrated in FIGS. 4, 6 and 8, includes anoverrange diaphragm 82, a chip carrier 84, a mounting sheet 86 (e.g.preferably epoxy), and a header 88. The illustrated header 88 has asubstantially circular solid main body 88A having a flat top face 88Bfrom which a series of transducer lead-out holes 88C and fill tube holes88D, 88E and 88F extend into the body 88A. Referring to FIG. 6, asubstantially rectangular cavity 88G forms a recess in an opposed bottomface 88H of the header 88. The illustrated header 88 has a first opening88D extending between the top face 88B and bottom face 88H; and a secondopening 88E that extends partly through the header body 88A andcommunicates with a transverse cross-bore opening 88I. A third opening88F, shown in FIG. 8, extends between the top face 88B and the bottomfaces 88H, similar to the first opening 88D.

As best shown in FIG. 8, the illustrated chip carrier 84 has adielectric body that mounts a pressure sensing element 89. For purposesof clarity, the illustrated sensor assembly 80 has the fill tube 92 inthe cross-sectional plane. A set of electrical contact pins 84B isconnected by wire bonds to contacts of the sensing element 89 andextends upwardly from the top surface 84C. U.S. Pat. No. 5,285,690,incorporated herein by this reference, describes further a sensorsub-assembly suitable for use as the chip carrier 84. In the illustratedembodiment, the sensing element top surface senses the fluid pressure inthe low pressure input, and the sensing element bottom surface sensesthe fluid pressure in the high pressure input. In another preferredembodiment, the high pressure and low pressure sides of the sensingelement can be electronically switched by a digital logic module thatoperates with software code stored in a memory, and typically housed inthe electronic housing 13 (FIGS. 1 and 2).

With further reference to FIGS. 4 and 6, the mounting sheet 86 seatsover the chip carrier top surface 84C, and when heated to a selectedelevated temperature, hermetically seals the chip carrier 84 to theheader 88. The chip carrier 84 and the sheet 86 mount within therectangular cavity 88G, and the electrical pins 84B extend upward andthrough the header holes 88C that aperture the top face 88B. Anelectrical insulator cap 90 preferably mounts over the pins 84B tocenter the pins within the chip carrier holes, and to electricallyisolate the pins from the header 88.

The overrange diaphragm 82, preferably formed with concentricconvolutions in registration with the convolutions of the floor 30D(FIG. 3) of the mounting portion 30, is secured as by welding along thecircular periphery, to the header bottom face 88H. The diameter of thediaphragm 82 is closely equal to the outer diameter of the header 88.

In the illustrated embodiment, the sensor assembly 80 seats in theannular mount 30C and the overrange diaphragm 82 overlies the firstpressure passageway 36. This configuration places the diaphragm 82proximate to both the chip carrier 84 and the housing 15. The sensorassembly 80 is secured and sealed to the mounting portion 30 by weldingthe header 88, along its upper peripheral edge, to the annular mount30C, with a weld 32, FIG. 8.

With this structure, the overrange diaphragm 82 is located proximate tothe chip carrier 84 and is subjected, on opposite sides, to pressuresresponsive to the same high and low pressures to which the sensingelement 89 is subjected. The overrange diaphragm 82 thus effectivelyprotects the sensing element 89 from overrange pressure conditions byflexing far enough during overrange to allow isolation diaphragms 46Aand 46B to bottom out against the convoluted recesses 41A and 41B,thereby limiting the range of excess pressure communicated to thesensing element.

Placing the overrange diaphragm 82 proximate to the housing 15 and tothe chip carrier 84 allows the body element 16 to be fabricated in avariety of ways. For example, the body element 16 can be a one-piecemachined casting, as illustrated. Alteratively, it can be constructedfrom multiple machined cast layers, similar to the pressure transmittermarketed by The Foxboro Company, USA, under the trade designation 843Differential Pressure Transducer. In addition, this integralconfiguration allows the process diaphragms to have different positions,e.g. planar as the diaphragms 46A and 46B in FIGS. 2-8, or bi-planar asdescribed below with reference to FIGS. 1, 9 and 10.

The overrange diaphragm 82 and the flame arrestors 68,70 produce a timeconstant analogous to an electrical RC time constant that dampens fluidnoise resulting from pipe vibrations, mechanical shocks, and likemechanical disturbances. The flame arrestors 68,70 have a combinedcharacteristic flow resistance preferably of about 500 (psi)(sec)/in³,and the overrange diaphragm 82 has a characteristic compliance orhydraulic capacitance preferably of about 0.0003 in³ /psi. The arrestors68,70 and the diaphragm 82 are, fluidwise, connected in series, andproduce, with these particular parameters, a hydraulic time constant ofabout 150 milliseconds. This time constant allows the sensor to havehigh sensitivity to the pressure being measured while significantlyattenuating high frequency perturbations, i.e., noise in the fluidsbeing measured.

Referring again to FIGS. 4 and 8, a fill tube 92 seats in the thirdopening 88F in the header 88, and a tube 94 seats in the second opening88E. A U-shaped tube 96 has one end that seats in the first opening 88Dand a second end that mounts to the protrusion 70A of the flame arrestor70. The fill tubes 92 and 94, and openings 88F and 88E, respectively,provide structure for filling the high and low pressure sides of thepressure transmitter 10 with fill fluid.

As noted above, the pressure transmitter 10 employs an incompressiblefill fluid, such as a relatively viscous hydraulic liquid, to couple tothe sensing element 89 pressure conditions it receives at the processdiaphragm 46A and 46B. With reference to FIGS. 6 and 8, the transmitter10 is filled with a fill fluid by evacuating the passages within thebody element 16 of the assembled housing 15 of the pressure transmitter10. Typically, vacuum adaptors are secured to the fill tubes 92 and 94to purge the apparatus of air, moisture, solvents, condensates orresidues. Fill fluid is then introduced to the evacuated passagesthrough these fill tubes. When the filling operation is complete, theends of the tubes located distal from the header top face 88B arecrimped and sealed closed. The fill fluid preferably passes into adefined low pressure side and a defined high pressure side of thetransmitter 10. By way of example, in the low pressure side, the fluidpasses from the fill tube 94 into the cross-bore opening 881, to thechip carrier top face 84C, which is illustrated as the transducer lowpressure side. The fill fluid further flows about the periphery of theheader 88 and into the pressure passageway 36, in which the flamearrestor 68 is seated. From the passageway 36, the fluid flows throughthe pressure opening 34 to the back side of the process diaphragm 46A,FIG. 8. The fill fluid for the designated high pressure side passes fromthe fill tube 92 and the opening 88F to the chip carrier bottom face84D, e.g., the transducer high pressure side, and through the opening88D and the U-tube 96. The fluid further flows through the axiallyextending bore 70C and the transverse cylindrical channel 70D of theflame arrestor 70, and into the pressure passageway 38. From thepressure passageway 38, the fill fluid flows through the second pressureopening 35 to the back side of the process diaphragm 46B.

One feature of the foregoing construction of the pressure transmitter 10is that it requires only a relatively small volume of fill fluid. Ithence operates with a relatively small quantity of fill fluid whichenhances the operating performance. The matched convoluted contours ofthe header bottom face 88H, of the overrange diaphragm 82 and of thefloor 30D of the mounting portion contribute to attaining this smallfill fluid space.

Referring to FIGS. 6 and 7, each pressure passageway 36 and 38 in thebody element 16 is in communication pressurewise with one recessedchamber 62 and 61, respectively. That is, the process fluid applied tochamber 61 acts on the process diaphragm 46B, which transfers processfluid pressure fluctuations to the sensing element 89 by way of the fillfluid in the pressure opening 35, in the passageway 38, and in theU-tube 96. Similarly, process fluid pressure fluctuations applied to thechamber 62 are transferred to the sensing element 89 by way of the fillfluid in the opening 34, in the passageway 36, and in the header opening88I.

During operation of the transmitter 10, the fill fluid in the pressureopenings 34, 35 and in the passageways 36, 38, communicates to thesensing element 89 the input process line pressures, applied via processports 24A, 24B (FIG. 3), that act on the planar isolation diaphragms at46A and 46B (FIG. 8). The sensing element 89 accordingly generates asignal, in response to the applied pressures, indicative of the pressuredifference between the two pressure inputs. The signal is processed byassociated electronic circuitry resident in the casing 13, FIG. 1, andan output signal can be displayed via the output display 12, or can beapplied to other external devices, e.g., a computer.

FIG. 9 shows, in disassembled and exploded form, a second and preferredembodiment of a bi-planar pressure transmitter 100 embodying furtherfeatures of the invention. The pressure transmitter 100, which receivestwo side-by-side pressure input lines like the transmitter 10 describedabove, has opposed pressure diaphragms instead of ones lying in the sameplane as in the transmitter 10. The pressure transmitter 100 includes aweb 102 that is clamped between elbow-type flanges 104 and 106. The webis preferably symmetrically centered in the transmitter 100, along afirst normally horizontal axis 108, and has a rounded periphery toreduce the number of sharp contours. The flanges form input pressureports 110 and 112, to which process connectors 114 and 116 typically arebolted. The transmitter 100 is illustrated as having a transducermounting portion 118 that seats a sensor assembly 120, similarrespectively to the mounting portion 30 and the sensor assembly 80 ofthe transmitter 10.

More particularly, the illustrated web 102, FIG. 9, has opposed andparallel first and second normally vertical surfaces 102A and 102B.Vertically spaced bolt holes 102C aperture the web 102 and extend,parallel to the axis 108 and transverse to a first, normally verticalaxis 340, between the two surfaces 102A and 102B. The normally verticalsurfaces 102A and 102B are recessed, preferably identically, with a setof concentric convolutions 102D. Each illustrated set of convolutionsforms a sinusoidal profile.

The web 102 has an integrally formed and upwardly-extending neck portion124 that mountingly connects to the transducer mounting portion 118. Theillustrated transducer mounting portion 118 is similar to the transducermounting portion 30 of FIG. 2, and has a first annular surface 118A anda second stepped concentric surface 118B. An upwardly extending tubularmount 118C is integral with the second surface 118B, and extends axiallyupward therefrom to be uppermost on the web. The surfaces 118A and 118Bare concentric with the axis 122, and the mount 118C is radially offsettherefrom. The illustrated transducer mounting portion 118 has threeintegral and circumferentially-spaced flared portions 118E, 118F, and118G. Flared portion 118G overlies the second pressure passageway 136and is apertured with a bore 118H that aligns with that passageway. Themount 118C preferably circumscribes the first pressure passageway 134.Within the tubular mount 118C, the second surface 118B forms a mountingfloor 118D that has an undulating contour, again preferably formed byconcentric convolutions.

An instrument casing 130 (FIG. 1) mounts on the transmitter web 102above the neck portion 124 by seating on a collar 132 that seats on theweb in the annular lip formed by the first surface 118A, and theperiphery of the stepped second surface 118B. In a preferred embodiment,the collar 132 is welded to the transducer mounting portion 118 of theweb 102 along this lip.

As also shown in FIG. 10, first and second pressure passageways 134 and136 open onto the second surface 118B of the mounting portion 118, andextend vertically within the web 102. The first and second pressurepassageways 134,136 communicate with transverse, i.e.horizontally-extending, first and second pressure openings 138 and 140,respectively, formed in the web 102. The pressure passageways 134 and136 and the openings 138 and 140 communicate the pressures applied tothe diaphragms 200A and 200B mounted at the opposed web faces 102A and102B, at the recesses, to the transducer mounting portion 118. Flamearrestors 142 and 144, similar to the flame arrestors of FIG. 4, seat inthe first and second pressure passageways 134 and 136, respectively.Those of ordinary skill will recognize that two flame arrestors may notalways be needed, particularly when all potential flame sources are onone side only of the sensor assembly 120.

Pressures applied to the input ports 110 and 112 of the flanges 106,104are coupled to the diaphragms and thus the convoluted recesses of theweb 102 with further structure, as now described with reference to FIGS.9 and 10. Each illustrated flange 104 and 106 is preferably a one-piecemachined metal casting and forms one input pressure port 110 and 112,respectively. A rear face of the flange 106 is recessed with a chamber106A, illustratively of substantial circular cross-section that overliesthe recessed convolutions 102D of the web surface 102A. Likewise, a rearface of the flange 104 is recessed with a chamber 104A that overlies therecessed convolutions (not shown) of the web surface 102B. Gasketgrooves, for example groove of flange 104,104B are concentric with thechambers 104A and 106A, respectively, and seat deformable gaskets 146.Bolt holes 104C and 106C extend through the flanges 104 and 106, inalignment with the bolt-holes 102C in the web 102, and receive bolts148,148. The illustrated transmitter 100 is assembled with two bolts148,148 that extend through the two flanges and through the web 102 andare secured by nuts 150,150.

Each illustrated flange 104 and 106 has two oppositely-disposed boltshrouds 104E, 104E, and 106E,106E, configured as shown, each of whichencloses and thereby shrouds the portion of a bolt 148 that extendsbeyond the web 102. Further, the web 102 encloses and thereby shroudsthe length of each bolt 148 which extends between the flanges. Theassembly of this bolt shrouding structure of the web 102 and of the twoflanges 104 and 106 forms a continuous enclosure over each bolt 148along the passage thereof between the three assembled parts 102,104 and106. The resultant full shrouding of each bolt 148,148 enhances theoperational safety of the pressure transmitter 100, including areduction of the potential to leak process fluids applied to thepressure ports 110 and 112, caused by unequal thermal expansion of thebolts and assembly.

Each illustrated pressure port 110 and 112 extends parallel with asecond normally-horizontal axis 152 that is perpendicular to the axes108 and 340. Each illustrated pressure port 110 and 112 opens at a sideperipheral surface of each flange 104,106, respectively, and which isillustrated in FIG. 9 as the surface that faces to the right.

With further reference to FIGS. 9 and 10, each illustrated flange104,106 has a pair of opposed peripheral faces 104F,104F and 106F,106F.A threaded passage 104G extends from each peripheral face 104F to thechamber 104A. The two passages 104G, 104G of the flange 104 are coaxialalong an axis parallel to the axis 152 and intersect the chamber 104A atopposite ends of a geometrical chord that is offset from a horizontaldiameter of the circular cross-section of the illustrated chamber 104A.

In the upright orientation of the flange 104 shown in FIGS. 9 and 12,the opposed passage 104G enters the chamber 104A below the middle of thechamber, e.g., below the horizontal diameter. Accordingly, the passage104G can function as the pressure port 110 to receive process fluid tobe measured and also can be used to drain liquid including condensatefrom the flange 104. The flange can, alternatively, be inverted so thatthe passage 104G is vertically above the middle of the chamber 104A asshown in FIG. 11, in which case one passage can be used to purge gasesthat can collect in the chambers. Likewise, the flange 106 has atransverse passageway formed therein identical to passage 104G of flange104, to assist in draining and in purging operations.

Operation for self-venting with liquids is shown in FIG. 11. Any gaseswill rise in chamber 104A and return to the process fluid in pipe 250.Similarly, when positioned as in FIG. 12, the flange 104 providesself-draining operation for gases, and liquid in chamber 106A and inconnecting passages returns to the process stream in pipe 250. Mostother orientations of the transmitter 130 (FIG. 1 ) also provide eitherself-draining or self-venting operation.

The opening of each passage 104G to a face 104F includes a recess forseating a mating protrusion in each process connector 114 and forseating a circular seal 160, when that passage functions as the pressureport 110. An optional filter screen can be mounted within each flange104, 106 to remove particulate matter present in the input processmedium. When the flange passage functions as a purge for gases, asillustrated in FIG. 11, a vent body 162 is threaded therein. The ventbody has a ventilation throughbore and a ventilation needle 164removably and replaceably seats in the bore for selectively closing itand, alternatively, opening it to purge fluids. The vent body allows anoperator to break vacuum and allow the chamber to drain. Either a ventbody or a vent plug can be used in ports 110, 112 depending on operatorneeds or transmitter orientation. Optionally, an additional vent bodycan be positioned at a further threaded hole (not shown) into thechamber in the rear of the flange 106I at location 106J to providefurther venting and draining flexibility.

The further structure of the flange faces 104F,104F includes recessingeach with threaded holes that receive bolts 166 for mounting a processconnector 114 at the pressure port 110. The threaded bolt holes extendinto each flange parallel with the axis 152. The process connector 114overlies the pressure port 110 and has through bolt-holes 168A and aninput passageway 168B, at locations complementary to the bolt-holes andto the passage 104G that forms the pressure port 110.

Thus, the illustrated flange 104 can be used in the upright orientationshown in FIG. 9 or in the inverted orientation, as desired and dependingon whether primarily liquid or vapor is to be vented. Further, theflange can be operated with either peripheral face 104F providing theinput port 110 and, alternatively, providing the venting port.

The flange 106 preferably is identical to and hence interchangeable withthe flange 104. The flange 106 hence has opposed faces 106F,106F, andopposed passages 106G, 106G for venting and for input porting. A processconnector 116 is mounted by bolting at the input port 112, and a ventbody 162, removably and replaceably seating a vent needle 164, isthreaded into the opposing passage 106G.

When the transmitter is assembled with both flanges 104, 106, installedfor venting gas or for draining liquid, installation of the transmitteroriented with 90° clockwise rotation about the axis 108, FIG. 9, willstill orient the flanges 104 and 106 either in a self-venting positionor in a self-draining position.

With further reference to FIG. 9 and to the assembled transmitter ofFIG. 10, the flange 106 has a pair of ribs 106H, 106H, each of whichforms part of one peripheral face 106F. The two ribs outwardly extendfrom the flange front face 106I, on opposite sides of the front face.The flange front face 106I (side opposite the chamber 106A) preferablyhas formed thereon an orientation indicator 107 that indicates whetherthe flange is oriented to purge gas or is inverted to drain liquid.Likewise, the flange 104 has a pair of ribs 104H, 104H and anorientation indicator.

The illustrated orientation indicator is located, on the flange face106I, corresponding to the location of the passages 106G, 106Goff-center relative to the chamber 106A. The illustrated orientationindicator 107 includes a boss located off-center on the flange 106, i.e.vertically off-center for the upright orientation of FIG. 9, andlineally extending horizontally for an upright flange orientation.

As also shown in the exploded view of FIG. 9, the pressure transmitter100 employs two diaphragm plates 258,258, configured complementary tothe surface 102A and 102B of the web 102. The diaphragm plates overliethe web faces 102A, 102B, thus covering the corrugated regions, e.g.region 102D, formed on both faces. Each diaphragm plate has punchedholes at locations complementary to the bolt-holes 102C. The diaphragmplates preferably form first and second bi-planar process diaphragms200A and 200B, FIG. 10. Weld plates 264,264, configured complementary tothe web surfaces 102A and 102B, overlie the exposed faces of thediaphragm plates 258. Each weld plate has a circular opening 264A havinga diameter D2 equal to or slightly smaller than the outer diameter ofthe convoluted regions 102D,102E. Each weld plate 264 hermetically sealsthe diaphragm plate 258 to the web 102, as by laser or other penetratingweld to the web 102 at the periphery of the plate 264 and at thecircumference of the opening 264A. The deformable gaskets 146,146 mountover the welds formed around the openings 264A. The diameter of eachgasket preferably is smaller than the diameter of the weld line at thecircumference of each opening 264A, to ensure that process fluid doesnot wet the weld connection.

The diameter of the circular chambers 104A, 106A is preferably equal toor slightly less than the diameter D2 of the weld plate openings 264A.In a preferred embodiment, each chamber 104A, 106A allows the inputprocess medium applied by one pressure input line to act upon the entireportion of the diaphragm plate overlying one convoluted region 102D,102E, i.e. the portion that is circumscribed by the chambers 104A, 106A.

Thus, in the assembled transmitter 100 (FIGS. 1 and 10), the illustratedaxial succession of weld plates 264,264, the diaphragm plates 258,258,and the gaskets 146,146 is secured between the web 102 and the twoflanges 104,106.

Referring again to FIG. 9, a sensor assembly 120, identical in structureand operational features to the sensor assembly 80 of FIG. 3, mounts inthe annular mount 118C. The sensor assembly 120 includes an overrangediaphragm 82, a chip carrier 84, an epoxy mounting sheet 86, and aheader 88. The illustrated header 88 has a substantially circular mainbody 88A having a flat top face 88B from which a series of transducerlead-out holes 88C and fill tube holes 88D, 88E, and 88F extend into thebody 88A. Referring to FIG. 10, a substantially rectangular cavity 88Grecesses an opposed bottom face 88H of the header 88. The illustratedheader 88 has a first opening 88D and a third opening 88F, both of whichextend between the header top and bottom faces 88B and 88H. A secondopening 88E extends partly through the header body 88A and communicateswith a crossbore opening 88I, which in turn communicates with the chipcarrier 84 by a substantially vertical bore 88J.

As best shown in FIG. 10, the illustrated chip carrier 84 has adielectric body that mounts a pressure sensing element 89. Similar tothe planar embodiment of FIGS. 2 through 8, this cross-sectional view ofthe sensor assembly 120 includes the fill tube 92 diagrammaticallyrelocated for clarity of discussion. A set of electrical pins 84B isconnected by wire bonds to the contacts of the sensing element 89 andextends upwardly from the top surface 84C.

As previously described with reference to FIGS. 4 and 6, the mountingsheet 86 seats over the chip carrier top surface 84C, and when heated toa selected elevated temperature, hermetically seals the chip carrier 84to the header 88. The chip carrier 84 and the sheet 86 mount within therectangular cavity 88G, and the electrical pins 84B extend upward andthrough the header holes 88C that aperture the top face 88B. Theelectrical insulator cap 90 preferably mounts over the pins 84B tocenter the pins within the chip carrier holes, and to electricallyisolate the pins from the header 88.

The overrange diaphragm 82, preferably formed with concentricconvolutions in registration with the circular ridges or convolutions ofthe floor 118D of the mounting portion 118C, is secured, for example, bywelding along the periphery, to the header bottom face 88H. The diameterof the diaphragm 82 is closely equal to the outer diameter of the header88.

In the illustrated embodiment of the bi-planar transmitter of FIG. 9,the sensor assembly 120 seats in the annular mount 118C and theoverrange diaphragm 82 overlies the first pressure passageway 134 (FIG.10). Similar to the planar embodiment of FIG. 6, this configurationplaces the diaphragm proximate to both the chip carrier 84 and thehousing 15. The sensor assembly 120 is then secured and sealed to theannular mount 118C.

An electrical contact plate 328, which assembles onto the header 88, hasa series of transducer holes 328A and a set of peripheral notches 328B,328C, and 328D. A flexible electrical cable 330 is coupled at one end tothe top plate 328 and extends upwardly therefrom. When the plate isproperly positioned for assembly, the notches 328B, 328C and 328D arealigned to receive the fill tubes 94, 96 and 92, respectively. Thetransducer holes 328A seat over the portions of the electrical pins thatextend beyond the insulator cap 90. The contact plate provides a secureelectrical connection to the electrical pins 84B and thus to the sensingelement 89. The flexible cable 330 carries the output electrical signalsgenerated by the sensing element in response to pressure differencesapplied to the diaphragms 200A and 200B, to the associated electroniccircuitry mounted within the casing 130.

Referring again to FIGS. 9 and 10, the fill tube 92 seats in the thirdopening 88F in the header 88, and the tube 94 seats in the secondopening 88E. The U-shaped tube 96 has one end that seats in the firstopening 88D and a second end that mounts to the protrusion 144A of theflame arrestor 144. The fill tubes 92 and 94, and openings 88F and 88E,respectively, provide structure for filling the high and low pressuresides of the transmitter 100 with fill fluids. In addition, FIG. 10illustrates that a potting material 276 is cast within the sleeve 132and embeds the sensor assembly 120 in the mount 118C. The pottingmaterial fills the volume within the sleeve 132 and protects the sensorassembly 120 and its associated electrical leads from mechanical shock,vibrations, and like disturbances, and excludes moisture and corrosiveagents.

As also shown in FIGS. 1 and 9, the illustrated casing 130 has a neck130A that seats over the sleeve 132 by threaded attachment thereto, andthat, in turn, carries a housing portion 130B. The housing portion 130Bpreferably is divided into first and second internal compartments (notshown) and has a sealed opening that extends between the compartments.The illustrated casing housing portion 130B has a removable andreplaceable cover 130H, 130H at each end, i.e. on the left side and onthe right side in FIG. 1, that is preferably sealed to the housing witha deformable gasket 182, to provide access to each internal compartment.The removable covers 130H, 130H allow a customer or maintenancepersonnel to connect the casing electronics to remote processingcircuitry, as well as allow access to the housing electronics fortesting and/or repair.

The flexible electrical cable 330, electrically connected at one end tothe sensor assembly 120, extends upwardly into the casing 130 throughthe neck 130A and connects to the housing electronics. Typically, onecover has an optical window (FIG. 2) through which an output display canbe viewed. In a preferred embodiment, the resident housing electronicsincludes resident software code and a receiver that allows a systemoperator, via a remote digital logic module transmitter, toelectronically switch the high and low pressure sides of the pressuretransmitter 100.

With reference to FIG. 1, the casing 130 can further include a bossstructure 131 having a threaded throughbore 131A that forms adormer-like structure. The boss structure 131 allows access to thecasing interior when it is necessary to perform field tests. Thethroughbore 131A provides structure through which the casing electronicscan be connected to the remote processing circuitry. A second bossstructure is present on the opposite side of the casing 130 as analternate connection port.

The structures of the illustrated embodiments attain pressuretransmitters that are compact, relatively lightweight and relatively lowin cost. The pressure transmitters can also mount a read-out displaypositioned for relatively easy viewing. Furthermore, at least onetransmitter embodiment attains large process diaphragms in a compacttransmitter size, i.e. positioning the fastener-receiving apertures atthe four corners of a non-square quadrilateral (FIG. 4) or by employingonly a pair of bolts along a vertical axis, as in the bi-planar design(FIGS. 1 and 9). These configurations accommodate large processdiaphragms without increasing the overall size of the transmitter.

It will thus be seen that the invention efficiently attains the objectsset forth above, among those made apparent from the precedingdescription. Since certain changes may be made in the aboveconstructions without departing from the scope of the invention, it isintended that all matter contained in the above description or shown inthe accompanying drawings be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are to cover allgeneric and specific features of the invention described herein, and allstatements of the scope of the invention which, as a matter of language,might be said to fall therebetween.

Having described the invention, what is claimed as new and desired to besecured by Letters Patent is:
 1. Pressure transmitter apparatuscomprisingA. unitary body means having, in a first orientation,(1)vertical surface means extending along a first vertical axis andapertured with first and second pressure openings disposed atsubstantially the same vertical location, and (2) transducer mountingmeans located, in said first orientation, above said pressure openings,B. diaphragm means forming first and second process diaphragmsrespectively closing said first and second pressure openings, C. flangemeans removably and replaceably secured to said body means overlyingsaid diaphragm means, said flange means forming first and secondpressure ports for coupling first and second pressure inputs to saidfirst and second process diaphragms, respectively, D. first and secondpressure passages vertically extending at least partly within said bodymeans for communicating respectively between said first and secondpressure openings and said transducer mounting means, E. flameretardation means disposed within at least one of said first and secondpressure passages and located above said pressure openings and at leastpartly within said unitary body means, for introducing a flame barrierbetween said transducer mounting means and said pressure openings, andF. a pressure sensor assembly coupled to said transducer mounting meansand disposed in fluid communication with at least one of said first andsecond pressure passages, and having overrange protection means forprotecting against an overrange pressure condition within at least oneof said pressure passages.
 2. Pressure transmitter apparatus accordingto claim 1 wherein said unitary body means has neck meansinterconnecting said mounting means with said vertical surface means forproviding thermal isolation therebetween.
 3. Pressure transmitterapparatus according to claim 1 wherein said unitary body means furthercomprises ribbed means forming structural stiffeners integral with saidunitary body means.
 4. Pressure transmitter apparatus according to claim1 further comprising circuit means connected with said pressure sensorassembly and selectively operable for electronically designating whichof said first and second pressure inputs is a high pressure input. 5.Pressure transmitter apparatus according to claim 1 wherein saidpressure sensor assembly compriseshousing means having opposed andsubstantially parallel first and second faces that are transverse tosaid first axis and that are axially spaced apart along said first axis,in said first orientation, and a pressure sensing element, located atleast partly between said first and second faces, for generating asignal in response to the difference in pressure between said first andsecond pressure inputs applied to said first and second pressure ports.6. Pressure transmitter according to claim 5 wherein said overrangeprotection means overlies said second face of said housing means and isarranged in fluid communication with said first and second pressurepassages, for protecting said pressure sensing element from an overrangepressure condition.
 7. Pressure transmitter according to claim 6 whereinsaid overrange protection means comprises an overrange diaphragm. 8.Pressure transmitter apparatus according to claim 1 wherein said unitarybody means further comprises support means for replaceably and removablycoupling said body means to an external support structure.
 9. Pressuretransmitter apparatus according to claim 1 wherein said vertical surfacemeans includes a pair of parallel surface elements, and said first andsecond pressure openings are oppositely arranged and substantiallyparallel to each other.
 10. Pressure transmitter apparatus according toclaim 9 wherein said flange means comprises cover means forming firstand second process covers overlying said first and second processdiaphragms, respectively, each said process cover being apertured withat least one fastener-receiving opening.
 11. Pressure transmitterapparatus according to claim 1 further comprisingplural bolt-typefastener means for removably and replaceably securing said flange meansto said body means, and first shroud means on said body means forshroudingly enclosing at least a selected length of each said bolt-typefastener means.
 12. Pressure transmitter apparatus according to claim 11wherein said flange means includes second shroud means for shroudinglyenclosing at least a selected length of each said bolt-type fastenermeans, said first and second shroud means, in combination, shroud theentire length of said fastener means.
 13. Pressure transmitter apparatusaccording to claim 1 wherein said vertical surface means is planar andwherein said first and second pressure openings are planar.
 14. Pressuretransmitter apparatus according to claim 13 wherein said flange meanscomprises unitary cover means forming a process cover overlying saidfirst and second process diaphragms, respectively.
 15. Pressuretransmitter apparatus according to claim 13 further comprising aperturemeans aperturing said vertical surface means and forming firstfastener-receiving apertures in said unitary body means, said firstapertures being located at least at two corners of a path bounding aparallelogram having an acute included angle.
 16. Pressure transmitteraccording to claim 1 wherein said flange means has a selectively closedthrough passage therein and is adapted to be invertably mountable oversaid vertical surface means in a draining position and alternatively ina purging position, for disposing said through passage for drainingliquid when mounted in said draining position and for disposing saidthrough passage for purging gas when mounted in said purging position.17. Pressure transmitter apparatus comprisingA. unitary body meanshaving, in a first orientation,(1) vertical surface means extendingalong a first vertical axis and apertured with first and second pressureopenings, and (2) transducer mounting means disposed, in said firstorientation, above said pressure openings, B. diaphragm means formingfirst and second process diaphragms respectively closing said first andsecond pressure openings and disposed below said mounting means, C.flange means removably and replaceably secured to said body meansoverlying said diaphragm means and disposed below said mounting means,said flange means forming first and second pressure ports for couplingfirst and second pressure inputs to said first and second processdiaphragms, respectively, D. first and second pressure passagesvertically extending at least partly within said body means forcommunicating respectively between said first and second pressureopenings and said transducer mounting means, and E. a pressure sensorassembly coupled to said transducer mounting means and disposed in fluidcommunication with at least one of said first and second pressurepassages, and having overrange protection means for protecting againstan overrange pressure condition within at least one of said pressurepassages.
 18. Pressure transmitter apparatus according to claim 17A.further comprising at least first and second fastener apertures, eachextending horizontally, when in said first orientation, through saidbody means and said flange means, said apertures being vertically spacedapart and disposed below said transducer mounting means and below saidsensor means, and B. first and second threaded fasteners, each passingwithin the same-numbered fastener aperture for securing said body meansand said flange means when assembled together.
 19. Pressure transmitterapparatus according to claim 19further comprising fastener shroudingmeans on each of said body means and said flange means and shroudinglyenclosing said fasteners in the aperture thereof throughout engagementwith said flange means and with said body means.
 20. Pressuretransmitter apparatus according to claim 17 further comprisingA. sealmeans engaged between said diaphragm means and said flange means forsealing each pressure port with respect to one process diaphragm, and B.first and second weld connections, each sealingly securing thesame-numbered process diaphragm to said body means at said same-numberedpressure opening, each said weld connection being isolated from contactwith fluids at said pressure inputs.
 21. Pressure transmitter apparatusaccording to claim 17 further comprisingfirst and second flame arrestormeans vertically disposed respectively in said first and second pressurepassages, for introducing flame barriers between said transducermounting means and said pressure openings.
 22. Pressure transmitterapparatus according to claim 17 wherein said flange means has aselectively closed through passage therein and is adapted to beinvertably mountable over said vertical surface means in a drainingposition and alternatively in a purging position, for disposing saidthrough passage for draining liquid when mounted in said drainingposition and for disposing said through passage for purging gas whenmounted in said purging position.
 23. Pressure transmitter apparatusaccording to claim 17 further comprising circuit means connected withsaid pressure sensor assembly and selectively operable forelectronically designating which of said first and second pressureinputs is a high pressure input.